The invention relates to wirebonding and, more particularly, to an apparatus and method for reduced downward force wirebonding of integrated circuits.
Recent advances in integrated circuit technology have brought about the incorporation of low dielectric constant (low-k) dielectrics into the devices. However, these copper/low-k materials are particularly susceptible to oxidation as the result of passivation damage, which is associated with activities such as handling, probing, and wirebonding. Wirebonding is the most common technology used in the electronic packaging industry for making electrical connections between the electrode pads on an integrated circuit chip and wires extending to a substrate providing external connections to the chip. Two examples of known wirebonding methods are xe2x80x9cball bondingxe2x80x9d and xe2x80x9cwedge bondingxe2x80x9d.
Ball bonding is a process by which a wire is fed through and protrudes from a capillary hole in a bonding head. An electric arc melts the protruding wire into a ball which then solidifies. The solidified ball is pressed and flattened onto a bond pad by a bonding head. The ball/bond pad surface interface is then subjected to ultrasonic vibrations to form an electrical bond therebetween. In wedge bonding, a wedge feeds a wire through a clamp. Ultrasonic energy may then be used to bond the wire to a contact surface to form a first bond. The wedge is raised, forming a wire loop, and moves to a second bond site where a second bond is formed. The clamp thereafter pivots away from the tool to break the wire at the second bond.
Both ball bonding and wedge bonding are techniques which involve the application of a downward or normal force directly on the bond surface in order to successfully achieve an electrically sound bond between the wire and the bond surface. However, the downward force applied to the bond surface can cause damage to a passivation layer, frequently resulting in the oxidation of underlying metal therein. It is desirable, therefore to provide a method and/or apparatus which operates to reduce the amount of downward force applied to a bond surface.
In an exemplary embodiment of the invention, a bond pad structure for an integrated circuit has a bondable base member for receiving a wire bonded thereon. A cavity is formed within the base member, with the cavity being configured to capture the wire therein. The cavity has a first open end having a first width and a second open end having a second width, with the first width being greater than second width. In a preferred embodiment, the cavity is tapered from one end to the opposite end, and is trapezoidally shaped. The base member is preferably comprised of an electrically conducting material, such as aluminum.